The present invention applies to motor vehicle components and more specifically to components that automatically measure tire pressure and warn the vehicle operator when the tire pressure reaches a dangerously low level.
Systems currently being used for automatic measurement of tire pressure include tire radius monitoring systems, common visual gauges, radio transmitter based systems and proximity transfer based systems. A radius monitoring system uses the vehicle's anti-lock braking system (ABS) to measure the changing radius of a vehicle tire. Logic within the ABS calculates a value for tire pressure based upon the measured tire radius. A radio transmitter based system includes a transmitter upon each vehicle wheel and a centralized receiver on the body of the vehicle.
As an example of a proximity transfer based system, U.S. Pat. No. 6,124,787 to Isakov et al., discloses a tire pressure monitoring system (TPMS) as installed in the drive train of a motor vehicle. The TPMS consists of four sensor transducers, each mounted to the inside or outside of a corresponding tire, and four receivers each mounted via brackets to the drivetrain at a distance of several centimeters away from the inner edge of the corresponding tire. The TPMS continuously monitors air pressure within each of the tires during motion of the motor vehicle through generation of an electromagnetic coupling between corresponding pairs of sensor transducers and receivers during an alignment that occurs between the transducers and receivers during each revolution of the tires. The sensor transducer is preferably mounted to an inner edge of the tire or on the rim of the tire and consists of a circuit including an inductor, a capacitor, and a switching element including a self-contained diaphragm, or sylfone for controlling the opening and closing of a switch.
A drawback to systems existing in the art are their cost and complexity. A simpler system is desirable. Also, there is a potential, in radio based transmission systems, for the radio signal from one wheel to be confused with the radio signal from a second wheel. Additionally, in existing proximity transfer systems, some or all of the signal being transferred can be lost or mistransferred.